Based on the field survey and the related analysis, using the fuzzy mathematical method, the natural hazard risk of debris flows is defined, and the rainfall index for debris flows in summer as a piecewise function, is devised. A debris flow early warning model based on comprehensive judgement is established. Identification and prediction experiments are made on the hazard risks of five debris flows with the model for precipitation of various levels. Taking the debris flow happened to the north of Jiegu, Qinghai Province on 29 July 2003 as an example, a preliminary validation is conducted